Method for Patterning Interconnects

ABSTRACT

Various patterning methods involved with manufacturing semiconductor devices are disclosed herein. A method for fabricating a semiconductor structure (for example, interconnects) includes forming a patterned photoresist layer over a dielectric layer. An opening (hole) is formed in the patterned photoresist layer. In some embodiments, a surrounding wall of the patterned photoresist layer defines the opening, where the surrounding wall has a generally peanut-shaped cross section. The opening in the patterned photoresist layer can be used to form an opening in the dielectric layer, which can be filled with conductive material. In some embodiments, a chemical layer is formed over the patterned photoresist layer to form a pair of spaced apart holes defined by the chemical layer, and an etching process is performed on the dielectric layer using the chemical layer as an etching mask to form a pair of spaced apart holes through the dielectric layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Patent Application Ser. No. 62/339,484, filed May 20, 2016, which is hereby incorporated by reference in its entirety.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experienced rapid growth. Technological advances in IC materials and design have produced generations of ICs. Each generation has smaller and more complex circuits than the previous generation. However, these advances have increased the complexity of processing and manufacturing ICs. For example, a semiconductor structure typically includes a metallization layer disposed over a substrate, where the metallization layer that provides interconnections to devices (such as transistors, capacitors, resistors, and/or other active and passive devices) formed on the substrate. An inter-metal dielectric (IMD) layer disposed over the typically includes interconnects (such as vertical interconnects) connected to conducive lines of the metallization layer.

When forming the interconnects in the IMD layer, various photolithographic and etching processes are performed to form an opening (which can include one or more holes) in the IMD layer, which is subsequently filled with a conductive material. Typically, a number of holes formed in the IMD layer equals a number of photolithographic and etching operations performed on the IMD layer. For example, a two patterning, two etching (2P2E) process is typically performed to form an opening in the IMD layer that includes two holes, a three patterning, three etching (3P3E) process is typically performed to form an opening in the IMD layer that includes three holes, a four patterning, four etching (4P4E) process is typically performed to form an opening in the IMD layer that includes four holes, and so on. Such processing is not only very inefficient, but also very costly. A need therefore exists for a process that can form openings (for example, having more than one hole) in semiconductor processing layers, such as the IMD layer, in a relatively efficient and cost effective manner.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIG. 1 is an exemplary flowchart illustrating a method for fabricating a semiconductor structure according to various aspects of the present disclosure.

FIG. 2A is a schematic sectional top view illustrating a stage in the fabrication of the semiconductor structure according to the method of FIG. 1, FIG. 2B is a schematic sectional view taken on line 2B-2B′ of FIG. 2A, and FIG. 2C is a schematic sectional view taken on line 2C-2C′ of FIG. 2A.

FIG. 3A is a schematic sectional top view illustrating another stage in the fabrication of the semiconductor structure according to the method of FIG. 1, FIG. 3B is a schematic sectional view taken on line 3B-3B′ of FIG. 3A, and FIG. 3C is a schematic sectional view taken on line 3C-3C′ of FIG. 3A.

FIG. 4A is a schematic sectional top view illustrating another stage in the fabrication of the semiconductor structure according to the method of FIG. 1, FIG. 4B is a schematic sectional view taken on line 4B-4B′ of FIG. 4A, and FIG. 4C is a schematic sectional view taken on line 4C-4C′ of FIG. 4A.

FIG. 5A is a schematic sectional top view illustrating another stage in the fabrication of the semiconductor structure according to the method of FIG. 1, FIG. 5B is a schematic sectional view taken on line 5B-5B′ of FIG. 5A, and FIG. 5C is a schematic sectional view taken on line 5C-5C′ of FIG. 5A.

FIG. 6A is a schematic sectional top view illustrating another stage in the fabrication of the semiconductor structure according to the method of FIG. 1, FIG. 6B is a schematic sectional view taken on line 6B-6B′ of FIG. 6A, and FIG. 6C is a schematic sectional view taken on line 6C-6C′ of FIG. 6A.

FIG. 7 is an exemplary flowchart illustrating another method for fabricating a semiconductor structure according to various aspects of the present disclosure.

FIG. 8A is a schematic sectional top view illustrating a stage in the fabrication of the semiconductor structure according to the method of FIG. 7, FIG. 8B is a schematic sectional view taken on line 8B-8B′ of FIG. 8A, and FIG. 8C is a schematic sectional view taken on line 8C-8C′ of FIG. 8A.

FIG. 9A is a schematic sectional top view illustrating another stage in the fabrication of the semiconductor structure according to the method of FIG. 7, FIG. 9B is a schematic sectional view taken on line 9B-9B′ of FIG. 9A, and FIG. 9C is a schematic sectional view taken on line 9C-9C′ of FIG. 9A.

FIG. 10A is a schematic sectional top view illustrating another stage in the fabrication of the semiconductor structure according to the method of FIG. 7, FIG. 10B is a schematic sectional view taken on line 10B-10B′ of FIG. 10A, and FIG. 10C is a schematic sectional view taken on line 10C-10C′ of FIG. 10A.

FIG. 11A is a schematic sectional top view illustrating another stage in the fabrication of the semiconductor structure according to the method of FIG. 7, FIG. 11B is a schematic sectional view taken on line 11B-11B′ of FIG. 11A, and FIG. 11C is a schematic sectional view taken on line 11C-11C′ of FIG. 11A.

FIG. 12 is an exemplary flowchart illustrating yet another method for fabricating a semiconductor structure according to various aspects of the present disclosure.

FIG. 13A is a schematic sectional top view illustrating another stage in the fabrication of the semiconductor structure according to the method of FIG. 13, FIG. 13B is a schematic sectional view taken on line 13B-13B′ of FIG. 13A, and FIG. 13C is a schematic sectional view taken on line 13C-13C′ of FIG. 13A.

FIG. 14A is a schematic sectional top view illustrating another stage in the fabrication of the semiconductor structure according to the method of FIG. 12, FIG. 14B is a schematic sectional view taken on line 14B-14B′ of FIG. 14A, and FIG. 14C is a schematic sectional view taken on line 14C-14C′ of FIG. 14A.

FIG. 15A is a schematic sectional top view illustrating another stage in the fabrication of the semiconductor structure according to the method of FIG. 12, FIG. 15B is a schematic sectional view taken on line 15B-15B′ of FIG. 15A, and FIG. 15C is a schematic sectional view taken on line 15C-15C′ of FIG. 15A.

FIG. 16A is a schematic sectional top view illustrating another stage in the fabrication of the semiconductor structure according to the method of FIG. 12, FIG. 16B is a schematic sectional view taken on line 16B-16B′ of FIG. 16A, and FIG. 16C is a schematic sectional view taken on line 16C-16C′ of FIG. 16A.

FIG. 17A is a schematic sectional top view illustrating another stage in the fabrication of the semiconductor structure according to the method of FIG. 12, FIG. 17B is a schematic sectional view taken on line 17B-17B′ of FIG. 17A, and FIG. 17C is a schematic sectional view taken on line 17C-17C′ of FIG. 17A.

FIG. 18 is an exemplary flowchart illustrating yet another method for fabricating a semiconductor structure according to various aspects of the present disclosure.

FIG. 19A is a schematic sectional top view illustrating another stage in the fabrication of the semiconductor structure according to the method of FIG. 18, FIG. 19B is a schematic sectional view taken on line 19B-19B′ of FIG. 19A, and FIG. 19C is a schematic sectional view taken on line 19C-19C′ of FIG. 19A.

FIG. 20A is a schematic sectional top view illustrating another stage in the fabrication of the semiconductor structure according to the method of FIG. 18, FIG. 20B is a schematic sectional view taken on line 20B-20B′ of FIG. 20A, and FIG. 20C is a schematic sectional view taken on line 20C-20C′ of FIG. 20A.

FIG. 21A is a schematic sectional top view illustrating another stage in the fabrication of the semiconductor structure according to the method of FIG. 18, FIG. 21B is a schematic sectional view taken on line 21B-21B′ of FIG. 21A, and FIG. 21C is a schematic sectional view taken on line 21C-21C′ of FIG. 21A.

FIG. 22A is a schematic sectional top view illustrating another stage in the fabrication of the semiconductor structure according to the method of FIG. 18, FIG. 22B is a schematic sectional view taken on line 22B-22B′ of FIG. 22A, and FIG. 22C is a schematic sectional view taken on line 22C-22C′ of FIG. 22A.

FIG. 23 is an exemplary flowchart illustrating yet another method for fabricating a semiconductor structure according to various aspects of the present disclosure.

FIG. 24A is a schematic sectional top view illustrating another stage in the fabrication of the semiconductor structure according to the method of FIG. 23, and FIG. 24B is a schematic sectional view taken on line 24B-24B′ of FIG. 24A.

FIG. 25A is a schematic sectional top view illustrating another stage in the fabrication of the semiconductor structure according to the method of FIG. 23, and FIG. 25B is a schematic sectional view taken on line 25B-25B′ of FIG. 25A.

FIG. 26A is a schematic sectional top view illustrating another stage in the fabrication of the semiconductor structure according to the method of FIG. 23, and FIG. 26B is a schematic sectional view taken on line 26B-26B′ of FIG. 26A.

FIG. 27A is a schematic sectional top view illustrating another stage in the fabrication of the semiconductor structure according to the method of FIG. 23, and FIG. 27B is a schematic sectional view taken on line 27B-27B′ of FIG. 27A.

FIG. 28A is a schematic sectional top view illustrating another stage in the fabrication of the semiconductor structure according to the method of FIG. 23, and FIG. 28B is a schematic sectional view taken on line 28B-28B′ of FIG. 28A.

FIG. 29 is an exemplary flowchart illustrating yet another method for fabricating a semiconductor structure according to various aspects of the present disclosure.

FIG. 30A is a schematic sectional top view illustrating another stage in the fabrication of the semiconductor structure according to the method of FIG. 29, and FIG. 30B is a schematic sectional view taken on line 30B-30B′ of FIG. 30A.

FIG. 31A is a schematic sectional top view illustrating another stage in the fabrication of the semiconductor structure according to the method of FIG. 29, and FIG. 31B is a schematic sectional view taken on line 31B-31B′ of FIG. 31A.

FIG. 32A is a schematic sectional top view illustrating another stage in the fabrication of the semiconductor structure according to the method of FIG. 29, and FIG. 32B is a schematic sectional view taken on line 32B-32B′ of FIG. 32A.

FIG. 33A is a schematic sectional top view illustrating another stage in the fabrication of the semiconductor structure according to the method of FIG. 29, and FIG. 33B is a schematic sectional view taken on line 33B-33B′ of FIG. 33A.

DETAILED DESCRIPTION

The present application relates to semiconductor devices and methods for manufacturing semiconductor devices, and more particularly, to methods for patterning interconnects of semiconductor devices. Various patterning methods disclosed herein form an opening (hole) through a dielectric layer, such as an inter-metal dielectric (IMD) layer for providing interconnects for a semiconductor device, using a single photolithographic and etching operation. In some embodiments, the opening includes at least two holes extending through the dielectric layer, which are fabricated using a single photolithographic and etching operation. Such methods significantly improve efficiency and cost of manufacturing semiconductor device, which typically use more than one photolithographic and etching operation to fabricate more than one interconnect (for example, often, a number of holes formed through the dielectric layer equals a number of photolithographic and etching operations required).

The following disclosure provides many different embodiments, or examples, for implementing different features of the subject matter provided. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly. It should be understood that additional operations can be provided before, during, and after the method, and some of the operations described can be replaced or eliminated for other embodiments of the method.

FIG. 1 is an exemplary flowchart illustrating a method 100 for fabricating a semiconductor structure according to various aspects of the present disclosure. At block 105, an inter-metal dielectric (IMD) layer is provided. At block 110, a first hardmask layer is formed over the IMD layer. At block 115, a patterned photoresist layer is formed over the first hardmask layer. The patterned photoresist layer has an opening formed therethrough, where the opening includes a pair of holes and a channel that interconnects the holes. At block 120, an etching process is performed on the first hardmask layer using the patterned photoresist layer as an etching mask to form an opening through the first hardmask layer. The opening in the first hard mask layer includes a pair of holes and a channel that interconnects the holes. A surrounding wall (formed by the patterned first hardmask layer) defines the holes and the channel in the first hardmask layer. At block 125, the patterned photoresist layer is removed. At block 130, a second hardmask layer is formed on the surrounding wall of the first hardmask layer. The second hardmask layer has an opening that forms a pair of spaced apart holes defined in the second hardmask layer. At block 135, an etching process is performed on the IMD layer using the first hardmask layer and the second hardmask layer as an etching mask. The etching process forms an opening in the IMD layer, where the opening includes a pair of spaced apart holes that extend through the IMD layer (for example, to a metallization layer). At block 140, the first hard mask layer and the second hardmask layer are removed. Additional steps can be provided before, during, and after method 100, and some of the steps described can be moved, replaced, or eliminated for additional embodiments of method 100.

FIG. 2A is a schematic sectional top view illustrating a stage in the fabrication of an exemplary semiconductor structure 200 according to the method 100 of FIG. 1, FIG. 2B is a schematic sectional view taken on line 2B-2B′ of FIG. 2A, and FIG. 2C is a schematic sectional view taken on line 2C-2C′ of FIG. 2A. The semiconductor structure 200 includes a metallization layer formed over a substrate (not shown), where the metallization layer includes an insulative layer 210 and a plurality of conductive lines (for example, a conductive line 220 a and a conductive line 220 b). The insulative layer 210 has a top surface and a bottom surface, where conductive lines 220 a, 220 b extend through the insulative layer from the bottom surface to the top surface. Examples of materials for the insulative layer 210 include, but are not limited to, SiC, SiCO, SiCN, another insulative material, or a combination thereof. In some embodiments, conductive lines 220 a, 220 b are formed in the insulative layer 210 by forming a plurality of holes (openings) through the insulative layer 210 (for example, extending from the top surface to the bottom surface of the insulative layer 210), and filling the holes in the insulative layer 210 (for example, by a sputtering process) with a conductive material, whereby the conductive material forms the conductive lines 220 a, 220 b. Examples of conductive material include, but are not limited to, Al, Cu, Ni, another metal material, polysilicon, or a combination thereof. In some embodiments, the conductive lines 220 a, 220 b are metal lines or poly lines, depending on design requirements for semiconductor structure 200. The conductive lines 220 a, 220 b are used to interconnect devices (for example, transistors, resistors, capacitors, diodes, and/or other active and/or passive devices) underlying the metallization layer.

An inter-metal dielectric (IMD) layer 230 is disposed over the metallization layer (here, insulative layer 210 and the conductive lines 220 a, 220 b). The IMD layer 230 is formed by a suitable deposition process, such as a chemical vapor deposition (CVD) process, a physical vapor deposition (PVD) process, an atomic layer deposition (ALD) process, another deposition process, a derivative thereof, or a combination thereof. The IMD layer 230 may be formed of low-k dielectric materials, such as carbon-containing low-k dielectric materials, which may further include silicon, oxygen, nitrogen, or a combination thereof.

As shown in FIG. 2B and FIG. 2C, a first hardmask layer 240 and a tri-layer resist stack 250 are formed in succession over the IMD layer 230. The first hardmask layer 240 is formed using a suitable deposition process. The deposition process is a CVD process, a PVD process, an ALD process, another deposition process, a derivative thereof, or a combination thereof. Examples of materials for the first hardmask layer 240 include, but are not limited to, SiN, SiCN, SiC, SiO,, TiN, TiO, TaN, or a combination thereof. The tri-layer resist stack 250 includes a bottom layer 250 a, a middle layer 250 b, and a patterned photoresist layer 260. In some embodiments, the bottom layer 250 a is an organic film, and the middle layer 250 b is a spin-on glass (SOG) layer. In some embodiments, the bottom layer 250 a is deposited by a spin-on process over the first hardmask layer 240 to provide, for example, anti-reflective properties and etch-stop functionality. In some embodiments, the middle layer 250 b is formed by depositing (for example, by a spin-on process) SiO₂ over the bottom layer 250 a.

An opening is formed through the patterned photoresist layer 260. In FIG. 2A, the opening has a generally peanut-shaped cross section. The opening includes a pair of holes (a hole 270 a and a hole 270 b) and a channel 280 that interconnects the hole 270 a and the hole 270 b. A surrounding wall 290 (defined by the patterned photoresist layer 260) defines the holes 270 a, 270 b and the channel 280 in the patterned photoresist layer 260. In some embodiments, the holes 270 a, 270 b in the patterned photoresist layer 260 have a hole pitch of about 300 Angstroms (Å) to about 1,000 Å and a hole width of about 200 Å to about 800 Å. In some embodiments, the channel 280 in the patterned photoresist layer 260 has a channel width of about 100 Å to about 500 Å. The patterned photoresist layer 260 is formed using a lithographic process. The lithographic process includes coating (for example, spin-on coating), soft baking, mask aligning, exposure, post exposure baking, developing, rinsing, drying (for example, hard baking), and other processes. Following the formation of the patterned photoresist layer 260, an after-development inspection (ADI) process can be performed, in which the patterned photoresist layer 260 is inspected for defects. If during the ADI process the patterned photoresist layer 260 is found to be defective, the patterned photoresist layer 260 is stripped, and the lithographic process is repeated to form a new patterned photoresist layer.

FIG. 3A is a schematic sectional top view illustrating another stage in the fabrication of the semiconductor structure 200 according to the method 100 of FIG. 1, FIG. 3B is a schematic sectional view taken on line 3B-3B′ of FIG. 3A, and FIG. 3C is a schematic sectional view taken on line 3C-3C′ of FIG. 3A. In FIGS. 3A-3C, the opening in patterned photoresist layer 260 is transferred to the first hardmask layer 240. For example, an opening is formed through the first hardmask layer 240. In FIG. 3A, the opening has a generally peanut-shaped cross section. The opening includes a pair of holes (a hole 370 a and a hole 370 b) and a channel 380 that interconnects the hole 370 a and the hole 370 b. A surrounding wall 390 (defined by the patterned first hardmask layer 240) defines the holes 370 a, 370 b and the channel 380 in the patterned first hardmask layer 240. In some embodiments, an etching process is performed to remove portions of the middle layer 250 b, the bottom layer 250 a, and the first hardmask layer 240 to expose the IMD layer 230. The etching process uses the patterned photoresist layer 260 as an etching mask. As such, the holes 370 a, 370 b in the patterned first hardmask layer 240 have a substantially same hole pitch and a substantially same hole width as the holes 270 a, 270 b in the patterned photoresist layer 260, and the channel 280 in the patterned first hardmask layer 240 has a substantially same channel width as the channel 280 in the patterned photoresist layer 260. The etching process is a dry etching process, another suitable anisotropic etching process, or a combination thereof. The etching process uses SCF₄, CH_(x)F_(y), C₄F₈, Cl₂, O₂, N₂, Ar, CH₄, another etching gas, or a combination thereof. In some embodiments, the etching process is conducted at a pressure of about 5 mTorr to about 50 mTorr. In some embodiments, the etching process is conducted at a bias voltage of about 10 Volts (V) to about 50 V. After patterning the first hardmask layer 240 (for example, following the formation of the holes 370 a, 370 b and the channel 380 in the first hardmask layer 240), the tri-layer resist stack 250 is removed by a strip process. In an example, the strip process is a wet strip process and is performed using, for example, hydrofluoric acid (HF). In another example, the strip process is a dry strip process and is performed using, for example, CH₃ or BF₃.

FIG. 4A is a schematic sectional top view illustrating another stage in the fabrication of the semiconductor structure 200 according to the method 1000 of FIG. 1, FIG. 4B is a schematic sectional view taken on line 4B-4B′ of FIG. 4A, and FIG. 4C is a schematic sectional view taken on line 4C-4C′ of FIG. 4A. In FIGS. 4A-4C, a second hardmask layer 410 is formed over the patterned first hardmask layer 240 and the IMD layer 230. As shown in FIG. 4B and FIG. 4C, the second hardmask layer 410 is formed over the first hardmask layer 240 and the IMD layer 230 in a conformal manner. That is, the second hardmask layer 410 that is on a top surface of the first hardmask layer 240, the second hardmask layer 410 that is on the surrounding wall 390 of the first hardmask layer 240, and the second hardmask layer 410 that is on the IMD layer 230, in an exemplary embodiment, all have a substantially same thickness. In some embodiments, the second hardmask layer 410 has a thickness at least half of the channel width of the channel 380 in patterned first hardmask layer 240, and thus the second hardmask layer 410 fills the channel 380. In some embodiments, the thickness of the second hardmask layer 410 is from about 50 Å to about 400 Å. In some embodiments, the thickness of the second hardmask layer 410 is from about 5 Å to about 100 Å. The second hardmask layer 410 is formed by a suitable deposition process, such as an ALD process, a CVD process, a PVD process, another suitable deposition process, or a combination thereof. Examples of materials for the second hardmask layer 410 include, but are not limited to, SiN, SiCN, SiC, SiO_(x), SiCO_(x), TiN, TiO, TaN, or a combination thereof. In some embodiments, the deposition process is conducted at a temperature of about 50° C. to about 450° C.

FIG. 5A is a schematic sectional top view illustrating another stage in the fabrication of the semiconductor structure 200 according to the method 100 of FIG. 1, FIG. 5B is a schematic sectional view taken on line 5B-5B′ of FIG. 5A, and FIG. 5C is a schematic sectional view taken on line 5C-5C′ of FIG. 5A. In FIGS. 5A-5C, portions of second hardmask layer 410 are removed, leaving portions of the second hardmask layer 410 within the opening in patterned first hardmask layer 240. In some embodiments, the second hardmask layer 410 disposed on the top surface of the first hardmask layer 240 and the second hardmask layer 410 that is on the IMD layer 230 are removed, leaving the second hardmask layer 410 that is on the surrounding wall 390 of the first hardmask layer 240 to form an opening in the patterned second hardmask layer 410. The opening includes a pair of spaced apart holes (a hole 570 a and a hole 570 b). In some embodiments, the holes 570 a, 570 b have a substantially same hole pitch as the holes 370 a, 370 b in the patterned first hardmask layer 240 and a hole width less than the hole width of the holes 370 a, 370 b in the patterned first hardmask layer 240. In some embodiments, the holes 570 a, 570 b in the second hardmask layer 410 have a hole width of about 100 Å to about 700 Å. The portions of the second hardmask layer 410 (for example, on the top surface of the first hardmask layer 240 and on the IMD layer 230) are removed using an etching process (for example, an etch back process). The etching process is a dry etching process, another suitable anisotropic etching process, or a combination thereof. The etching process uses SCF₄, CH_(x)F_(y), C₄F₈, Cl₂, O₂, N₂, Ar, CH₄, another etching gas, or a combination thereof. In some embodiments, the etching process is conducted at a pressure of about 5 mTorr to about 50 mTorr. In some embodiments, the etching process is conducted at a bias voltage of about 10 V to about 50 V.

FIG. 6A is a schematic sectional top view illustrating another stage in the fabrication of the semiconductor structure 200 according to the method 100 of FIG. 1, FIG. 6B is a schematic sectional view taken on line 6B-6B′ of FIG. 6A, and FIG. 6C is a schematic sectional view taken on line 6C-6C′ of FIG. 6A. In FIGS. 6A-6C, the opening in patterned second hardmask layer 410 is transferred to the IMD layer 230. For example, an opening is formed through the IMD layer 230. The opening includes a pair of spaced apart holes (a hole 670 a and a hole 670 b) formed through the IMD layer 230. An etching process is performed to remove portions of the IMD layer 230, forming the holes 670 a, 670 b that respectively expose conductive lines 220 a, 220 b. The etching process uses the first hardmask layer 240 and the second hardmask layer 410 as an etching mask. In some embodiments, the holes 670 a, 670 b in the IMD layer 230 have a substantially same hole pitch and a substantially same hole width as the holes 570 a, 570 b in the patterned second hardmask layer 410. After patterning the IMD layer 230 (for example, to form the holes 670 a, 670 b in the IMD layer 230), the first hardmask layer 240 and the second hardmask layer 410 are removed by an etching process. The etching process is a wet etch process, a dry etch process, another suitable etch process, or a combination thereof.

Following the removal of the first hardmask layer 240 and the second hardmask layer 410, the opening in the IMD layer 230 (for example, holes 670 a, 670 b) may be filled with a conductive material. In some embodiments, a sputtering process forms a conductive material over IMD layer 230 that fills the holes 670 a, 670 b. In some embodiments, the conductive material is Al, Cu, Ni, another metal material, or a combination thereof. Thereafter, a chemical mechanical planarizing (CMP) process may be performed to remove the excess conductive material, such as conductive material formed on a top surface of the IMD layer 230. The conductive material remaining in the holes 670 a, 670 b serves as vertical interconnects. For example, in some embodiments, the semiconductor structure 200 can include vertical interconnects formed in the IMD layer 230, such as a vertical interconnect (formed by conductive material filling the hole 670 a) to conductive line 220 a and a vertical interconnect (formed by conductive material filling the hole 670 b) to conductive line 220 b.

FIG. 7 is another exemplary flowchart illustrating a method 700 for fabricating a semiconductor structure according to various aspects of the present disclosure. At block 710, an IMD layer is provided. At block 720, a hardmask layer is formed over the IMD layer. At block 730, a patterned photoresist layer is formed over the hardmask layer. The patterned photoresist layer includes an opening that includes a pair of holes and a channel that interconnects the holes. A surrounding wall defines the holes and the channel in the patterned photoresist layer. At block 740, a chemical layer is formed on a top surface and the surrounding wall of the patterned photoresist layer to form a pair of spaced apart holes defined thereby. At block 750, an etching process is performed on the hardmask layer using the chemical layer as an etching mask to form a pair of spaced apart holes through the hardmask layer. At block 760, the patterned photoresist layer and the chemical layer are removed. At block 770, an etching process is performed on the IMD layer using the hardmask layer as an etching mask to form a pair of spaced apart holes through the IMD layer. At block 780, the hardmask layer is removed. Additional steps can be provided before, during, and after method 700, and some of the steps described can be moved, replaced, or eliminated for additional embodiments of method 700.

FIG. 8A is a schematic sectional top view illustrating a stage in the fabrication of an exemplary semiconductor structure 800 according to the method 700 of FIG. 7, FIG. 8B is a schematic sectional view taken on line 8B-8B′ of FIG. 8A, and FIG. 8C is a schematic sectional view taken on line 8C-8C′ of FIG. 8A. The semiconductor structure 800 includes a metallization layer formed over a substrate (not shown), where the metallization layer includes an insulative layer 810 and a plurality of conductive lines (for example, a conductive line 820 a and a conductive line 820 b). The insulative layer 810 has a top surface and a bottom surface, where conductive lines 820 a, 820 b extend through the insulative layer from the bottom surface to the top surface. Examples of materials for the insulative layer 810 include, but are not limited to, SiC, SiCO, SiCN, another insulative material, or a combination thereof. In some embodiments, conductive lines 820 a, 820 b are formed in the insulative layer 810 by forming a plurality of holes (openings) through the insulative layer 810 (for example, extending from the top surface to the bottom surface of the insulative layer 810), and filling the holes in the insulative layer 810 (for example, by a sputtering process) with a conductive material, whereby the conductive material forms the conductive lines 820 a, 820 b. Examples of conductive material include, but are not limited to, Al, Cu, Ni, another metal material, polysilicon, or a combination thereof. In some embodiments, the conductive lines 820 a, 820 b are metal lines or poly lines, depending on design requirements for semiconductor structure 800. The conductive lines 820 a, 820 b are used to interconnect devices (for example, transistors, resistors, capacitors, diodes, and/or other active and/or passive devices) underlying the metallization layer.

An inter-metal dielectric (IMD) layer 830 is disposed over the metallization layer (here, the insulative layer 810 and the conductive lines 820 a, 820 b). The IMD layer 830 is formed by a suitable deposition process, such as a chemical vapor deposition (CVD) process, a physical vapor deposition (PVD) process, an atomic layer deposition (ALD) process, another deposition process, a derivative thereof, or a combination thereof. The IMD layer 830 may be formed of low-k dielectric materials, such as carbon-containing low-k dielectric materials, which may further include silicon, oxygen, nitrogen, or a combination thereof.

As shown in FIG. 8B and FIG. 8C, a hardmask layer 840 and a tri-layer resist stack 850 are formed in succession over the IMD layer 830. The hardmask layer 840 is formed using a suitable deposition process, such as a CVD process, a PVD process, an ALD process, another deposition process, a derivative thereof, or a combination thereof. Examples of materials for the hardmask layer 840 include, but are not limited to, SiN, SiCN, SiC, SiO,, TiN, TiO, TaN, or a combination thereof. The tri-layer resist stack 850 includes a bottom layer 850 a, a middle layer 850 b, and a patterned photoresist layer 860. In some embodiments, the bottom layer 850 a is an organic film, and the middle layer 850 b is a spin-on glass (SOG) layer. In some embodiments, the bottom layer 850 a is deposited by a spin-on process over the hardmask layer 840 to provide, for example, anti-reflective properties and etch-stop functionality. In some embodiments, the middle layer 850 b is formed by depositing (for example, by a spin-on process) SiO₂ over the bottom layer 850 a.

An opening is formed through the patterned photoresist layer 860. In FIG. 8A, the opening has a generally peanut-shaped cross section. The opening includes a pair of holes (a hole 870 a and a hole 870 b) and a channel 880 that interconnects the hole 870 a and the hole 870 b. A surrounding wall 890 (defined by the patterned photoresist layer 860) defines the holes 870 a, 870 b and the channel 880 in the patterned photoresist layer 860. In some embodiments, the holes 870 a, 870 b in the patterned photoresist layer 860 have a hole pitch of about 300 Å to about 1,000 Å and a hole width of about 200 Å to about 800 Å. In some embodiments, the channel 880 in the patterned photoresist layer 860 has a channel width of about 100 Å to about 500 Å. The patterned photoresist layer 860 is formed using a lithographic process. The lithographic process includes coating (for example, spin-on coating), soft baking, mask aligning, exposure, post exposure baking, developing, rinsing, drying (for example, hard baking), and other processes. Following the formation of the patterned photoresist layer 860, an ADI process can be performed, in which the patterned photoresist layer 860 is inspected for defects. If during the ADI process the patterned photoresist layer 860 is found to be defective, the patterned photoresist layer 860 is stripped, and the lithographic process is repeated to form a new patterned photoresist layer.

FIG. 9A is a schematic sectional top view illustrating another stage in the fabrication of the semiconductor structure 800 according to the method 700 of FIG. 7, FIG. 9B is a schematic sectional view taken on line 9B-9B′ of FIG. 9A, and FIG. 9C is a schematic sectional view taken on line 9C-9C′ of FIG. 9A. In FIGS. 9A-9C, a chemical layer 910 having an opening therein is formed over the patterned photoresist layer 860. The opening includes a pair of spaced apart holes (a hole 970 a and a hole 970 b) defined by the chemical layer 910. For example, the chemical layer 910 is formed on exposed surfaces of the patterned photoresist layer 860, such as a top surface of the patterned photoresist layer 860 and a surface of the patterned photoresist layer 860 that defines the surrounding wall 890. In some embodiments, the holes 970 a, 970 b have a substantially same hole pitch as the holes 870 a, 870 b in the patterned photoresist layer 860. In some embodiments, the holes 970 a, 970 b (defined in the chemical layer 910) have a hole width less than the hole width of the holes 870 a, 870 b in the patterned photoresist layer 860. In some embodiments, the holes 970 a, 970 b have a hole width of about 100 Å to about 700 Å. In some embodiments, as depicted in FIG. 9B and FIG. 9C, the chemical layer 910 on the top surface of the patterned photoresist layer 860 has a substantially same thickness as the chemical layer 910 on the surface of the patterned photoresist layer 860 that defines the surrounding wall 890. In some embodiments, the chemical layer 910 has a thickness at least half of the channel width of the channel 880 in the patterned photoresist layer 860. In some embodiments, the thickness of the chemical layer 910 is about 50 Å to about 400 Å.

The chemical layer 910 is formed by any suitable process. In some embodiments, forming the chemical layer 910 includes: forming a shrink material over exposed portions of the tri-layer resist stack 850 (for example, over exposed portions of the patterned photoresist layer 860 and exposed portions of the middle layer 850 b, such that the shrink material fills the holes 870 a, 870 b defined in the patterned photoresist layer 860); baking the shrink material, such that the shrink material reacts with the patterned photoresist layer 860 to form the chemical layer 910; and removing an unreacted portion of the shrink material (for example, portions of the shrink material on the middle layer 850 b), such that the holes 970 a, 970 b are formed through the chemical layer 910. In some embodiments, the shrink material is formed over the patterned photoresist layer 860 and middle layer 850 b (for example, over the holes 870 a, 870 b defined in the patterned photoresist layer 860) using a suitable spin-on process. In some embodiments, the shrink material is baked at a baking temperature of about 110° C. to about 170° C. In some embodiments, the shrink material is baked for about 60 seconds. The unreacted portion of the shrink material is removed using a suitable development process. In some embodiments, the development process includes a puddle development process (for example, where the unreacted portion of the shrink material is washed away with water (for example, de-ionized water (DIW) for about 60 seconds)), an immersion development process, a spray development process, another suitable development process, or a combination thereof. The shrink material includes an inorganic material (such as a dielectric material), an organic material (such as a polymeric material), or a combination thereof. In some embodiments, an example of a water soluble organic material that may be used as the shrink material is commercially available from Dow Chemical Corporation or JSR Corporation. In some embodiments, the shrink material is a topaz-type material, such as that commercially available from Applied Materials, Santa Clara, Calif. In some embodiments, the shrink material is an inter-mixing type polymer.

FIG. 10A is a schematic top view illustrating another stage in the fabrication of the semiconductor structure 800 according to the method 700 of FIG. 7, FIG. 10B is a schematic sectional view taken on line 10B-10B′ of FIG. 10A, and FIG. 10C is a schematic sectional view taken on line 10C-10C′ of FIG. 10A. In FIGS. 10A-10C, the opening in patterned chemical layer 910 is transferred to the hardmask layer 840. For example, an opening is formed through the hardmask layer 840. In FIG. 10A, the opening includes a pair of space apart holes (a hole 1070 a and a hole 1070 b). In some embodiments, an etching process is performed to remove portions of the middle layer 850 b, the bottom layer 850 a, and the hardmask layer 840 to expose the IMD layer 830. The etching process uses the patterned chemical layer 910 as an etching mask. As such, the holes 1070 a, 1070 b in the patterned hardmask layer 840 have a substantially same hole pitch and a substantially same hole width as the holes 970 a, 970 b in the chemical layer 910. The etching process is a dry etching process, another suitable anisotropic etching process, or a combination thereof. The etching process uses SCF₄, CH_(x)F_(y), C₄F₈, Cl₂, O₂, N₂, Ar, CH₄, another etching gas, or a combination thereof. In some embodiments, the etching process is conducted at a pressure of about 5 mTorr to about 50 mTorr. In some embodiments, the etching process is conducted at a bias voltage of about 10 V to about 50 V. After patterning the hardmask layer 840 (for example, following the formation of the holes 1070 a, 1070 b in the hardmask layer 840), the tri-layer resist stack 850 is removed by a strip process, thereby removing the chemical layer 910. In an example, the strip process is a wet strip process and is performed using, for example, hydrofluoric acid (HF). In another example, the strip process is a dry strip process and is performed using, for example, CH₃ or BF₃.

FIG. 11A is a schematic top view illustrating another stage in the fabrication of the semiconductor structure 800 according to the method 700 of FIG. 7, FIG. 11B is a schematic sectional view taken on line 11B-11B′ of FIG. 11A, and FIG. 11C is a schematic sectional view taken on line 11C-11C′ of FIG. 11A. In FIGS. 11A-11C, the opening in patterned hardmask layer 840 is transferred to the IMD layer 830. For example, an opening is formed through the IMD layer 830. The opening includes a pair of spaced apart holes (a hole 1170 a and a hole 1170 b) formed through the IMD layer 830. An etching process is performed to remove portions of the IMD layer 830, forming the holes 1170 a, 1170 b that respectively expose conductive lines 820 a, 820 b. The etching process uses the hardmask layer 840 as an etching mask. In some embodiments, the holes 1170 a, 1170 b in the IMD layer 830 have a substantially same hole pitch and a substantially same hole width as the holes 1070 a, 1070 b in the patterned hardmask layer 840. After patterning the IMD layer 830 (for example, to form the holes 1170 a, 1170 b in the IMD layer 830), the hardmask layer 840 is removed by an etching process. The etching process is a wet etch process, a dry etch process, another suitable etch process, or a combination thereof.

Following the removal of the hardmask layer 840, the opening in the IMD layer 830 (for example, holes 1170 a, 1170 b) may be filled with a conductive material. In some embodiments, a sputtering process forms a conductive material over the IMD layer 830 that fills the holes 1170 a, 1170 b. In some embodiments, the conductive material is Al, Cu, Ni, another metal material, or a combination thereof. Thereafter, a chemical mechanical planarizing (CMP) process may be performed to remove the excess conductive material, such as conductive material formed on a top surface of the IMD layer 830. The conductive material remaining in the holes 1170 a, 1170 b serves as vertical interconnects. For example, in some embodiments, the semiconductor structure 800 can include vertical interconnects formed in the IMD layer 830, such as a vertical interconnect (formed by conductive material filling the hole 1170 a) to conductive line 820 a and a vertical interconnect (formed by conductive material filling the hole 1170 b) to conductive line 820 b.

FIG. 12 is another exemplary flowchart illustrating a method 1200 for fabricating a semiconductor structure according to various aspects of the present disclosure. At block 1210, an IMD layer is provided. At block 1220, a first hardmask layer is formed over the IMD layer. At block 1230, a patterned photoresist layer is formed over the first hardmask layer. The patterned photoresist layer has an opening formed therethrough, where the opening includes three holes and a pair of channels, each of which interconnects an adjacent pair of the holes. At block 1240, an etching process is performed on the first hardmask layer using the patterned photoresist layer as an etching mask to form an opening in through the first hardmask layer. The opening in the first hardmask layer includes three holes and a pair of channels, each of which interconnects an adjacent pair of the holes. A surrounding wall (formed by the patterned first hardmask layer) defines the holes and the channels in the first hardmask layer. At block 1250, the patterned photoresist layer is removed. At block 1260, a second hardmask layer is formed on the surrounding wall of the first hardmask layer. The second hardmask layer has an opening the forms three spaced apart holes defined in the second hardmask layer. At block 1270, an etching process is performed on the IMD layer using the first hardmask and the second hardmask layer as an etching mask. The etching process forms an opening in the IMD layer, where the opening includes three spaced apart holes that extend through the IMD layer (for example, to a metallization layer). At block 1280, the first hard mask layer and the second hardmask layer are removed. Additional steps can be provided before, during, and after method 1200, and some of the steps described can be moved, replaced, or eliminated for additional embodiments of method 1200.

FIG. 13A is a schematic sectional top view illustrating a stage in the fabrication of an exemplary semiconductor structure 1300 according to the method 1200 of FIG. 12, FIG. 13B is a schematic sectional view taken on line 13B-13B′ of FIG. 13A, and FIG. 13C is a schematic sectional view taken on line 13C-13C′ of FIG. 13A. The semiconductor structure 1300 includes a metallization layer formed over a substrate (not shown), where the metallization layer includes an insulative layer 1310 and a plurality of conductive lines (for example, a conductive line 1320 a, a conductive line 1320 b, and a conductive line 1320 b). The insulative layer 1310 has a top surface and a bottom surface, where conductive lines 1320 a, 1320 b extend through the insulative layer from the bottom surface to the top surface. Examples of materials for the insulative layer 1310 include, but are not limited to, SiC, SiCO, SiCN, another insulative material, or a combination thereof. In some embodiments, conductive lines 1320 a, 1320 b, 1320 c are formed in the insulative layer 1310 by forming a plurality of holes (openings) through the insulative layer 1310 (for example, extending from the top surface to the bottom surface of the insulative layer 1310), and filling the holes in the insulative layer 1310 (for example, by a sputtering process) with a conductive material, whereby the conductive material forms the conductive lines 1320 a, 1320 b, 1320 c. Examples of conductive material include, but are not limited to, Al, Cu, Ni, another metal material, polysilicon, or a combination thereof. In some embodiments, the conductive lines 1320 a, 1320 b, 1320 c are metal lines or poly lines, depending on design requirements for semiconductor structure 1300. The conductive lines 1320 a, 1320 b, 1320 c are used to interconnect devices (for example, transistors, resistors, capacitors, diodes, and/or other active and/or passive devices) underlying the metallization layer.

An inter-metal dielectric (IMD) layer 1330 is disposed over the metallization layer (here, insulative layer 1310 and the conductive lines 1320 a, 1320 b, 1320 c). The IMD layer 1330 is formed by a suitable deposition process, such as a CVD process, a PVD process, an ALD process, another deposition process, a derivative thereof, or a combination thereof. The IMD layer 1330 may be formed of low-k dielectric materials, such as carbon-containing low-k dielectric materials, which may further include silicon, oxygen, nitrogen, or a combination thereof.

As shown in FIG. 13B and FIG. 13C, a first hardmask layer 1340 and a tri-layer resist stack 1350 are formed in succession over the IMD layer 1330. The first hardmask layer 1340 is formed using a suitable deposition process. The deposition process is a CVD process, a PVD process, an ALD process, another deposition process, a derivative thereof, or a combination thereof. Examples of materials for the first hardmask layer 1340 include, but are not limited to, SiN, SiCN, SiC, SiO,, TiN, TiO, TaN, or a combination thereof. The tri-layer resist stack 1350 includes a bottom layer 1350 a, a middle layer 1350 b, and a patterned photoresist layer 1360. In some embodiments, the bottom layer 1350 a is an organic film, and the middle layer 250 b is a spin-on glass (SOG) layer. In some embodiments, the bottom layer 1350 a is deposited by a spin-on process over the first hardmask layer 1340 to provide, for example, anti-reflective properties and etch-stop functionality. In some embodiments, the middle layer 250 b is formed by depositing (for example, by a spin-on process) SiO₂ over the bottom layer 250 a.

An opening is formed through the patterned photoresist layer 1360. In FIG. 13A, the opening includes three holes (a hole 1370 a, a hole 1370 b, and a hole 1370 c) sequentially disposed along a length of the patterned photoresist layer 1360, where a channel 1380 a interconnects the hole 1370 a and the hole 1370 b and a channel 1380 b interconnects the hole 1370 b and the hole 1370 c. A surrounding wall 1390 (defined by the patterned photoresist layer 1360) defines the holes 1370 a, 1370 b, 1370 c and the channels 1380 a, 1380 b in the patterned photoresist layer 1360. In some embodiments, the holes 1370 a, 1370 b, 1370 c in the patterned photoresist layer 1360 have a hole pitch of about 300 Å to about 1,000 Å and a hole width of about 200 Å to about 800 Å. In some embodiments, the channels 1380 a, 1380 b in the patterned photoresist layer 1360 have a channel width of about 100 Å to about 500 Å. The patterned photoresist layer 1360 is formed using a lithographic process. The lithographic process includes coating (for example, spin-on coating), soft baking, mask aligning, exposure, post exposure baking, developing, rinsing, drying (for example, hard baking), and other processes. Following the formation of the patterned photoresist layer 1360, an ADI process can be performed, in which the patterned photoresist layer 1360 is inspected for defects. If during the ADI process the patterned photoresist layer 1360 is found to be defective, the patterned photoresist layer 1360 is stripped, and the lithographic process is repeated to form a new patterned photoresist layer.

FIG. 14A is a schematic sectional top view illustrating another stage in the fabrication of the semiconductor structure 1300 according to the method 1200 of FIG. 12, FIG. 14B is a schematic sectional view taken on line 14B-14B′ of FIG. 14A, and FIG. 14C is a schematic sectional view taken on line 14C-14C′ of FIG. 14A. In FIGS. 14A-14C, the opening in patterned photoresist layer 1360 is transferred to the first hardmask layer 1340. For example, an opening is formed through the first hardmask layer 1340. In FIG. 14A, the opening includes three holes (a hole 1470 a, a hole 1470 b, and a hole 1470 c) that are sequentially disposed along a length of the first hardmask layer 1340. A channel 1480 a interconnects the hole 1470 a and the hole 1470 b, and a channel 1480 b interconnects the hole 1470 b and the hole 1470 c. A surrounding wall 1490 (defined by the patterned first hardmask layer 1340) defines the holes 1470 a, 1470 b, 1470 c and the channels 1480 a, 1480 b in the patterned first hardmask layer 1340. In some embodiments, an etching process is performed to remove portions of the middle layer 1350 b, the bottom layer 1350 a, and the first hardmask layer 1340 to expose the IMD layer 1330. The etching process uses the patterned photoresist layer 1360 as an etching mask. As such, the holes 1470 a, 1470 b, 1470 c in the first hardmask layer 1340 have a substantially same hole pitch and a substantially same hole width as the holes 1370 a, 1370 b, 1370 c in the patterned photoresist layer 1360, and the channels 1480 a, 1480 b in the first hardmask layer 1340 have a substantially same channel width as the channels 1380 a, 1380 b in the patterned photoresist layer 1360. The etching process is a dry etching process, another suitable anisotropic etching process, or a combination thereof. The etching process uses SCF₄, CH_(x)F_(y), C₄F₈, Cl₂, O₂, N₂, Ar, CH₄, another etching gas, or a combination thereof. In some embodiments, the etching process is conducted at a pressure of about 5 mTorr to about 50 mTorr. In some embodiments, the etching process is conducted at a bias voltage of about 10 Volts to about 50 Volts. After patterning the first hardmask layer 1340 (for example, following the formation of the holes 1470 a, 1470 b, 1470 c and the channels 1480 a, 1480 b in the first hardmask layer 1340), the tri-layer resist stack 1350 is removed by a strip process. In an example, the strip process is a wet strip process and is performed using, for example, hydrofluoric acid (HF). In another example, the strip process is a dry strip process and is performed using, for example, CH₃ or BF₃.

FIG. 15A is a schematic sectional top view illustrating another stage in the fabrication of the semiconductor structure 1300 according to the method 1200 of FIG. 12, FIG. 15B is a schematic sectional view taken on line 15B-15B′ of FIG. 15A, and FIG. 15C is a schematic sectional view taken on line 15C-15C′ of FIG. 15A. In FIGS. 15A-15C, a second hardmask layer 1510 is formed over the first hardmask layer 1340 and the IMD layer 1330. As shown in FIG. 15B and FIG. 15C, the second hardmask layer 1510 is formed over the first hardmask layer 1340 and the IMD layer 1330 in a conformal manner. That is, the second hardmask layer 1510 that is on a top surface of the first hardmask layer 1340, the second hardmask layer 1510 that is on the surrounding wall 1490 of the first hardmask layer 1340, and the second hardmask layer 1510 that is on the IMD layer 1330, in an exemplary embodiment, all have a substantially same thickness. In some embodiments, the second hardmask layer 1510 has a thickness at least half of the channel width of the channels 1480 a, 1480 b in the first hardmask layer 1340, and thus the second hardmask layer 1510 fills the channels 1480 a, 1480 b in the first hardmask layer 1340. In an exemplary embodiment, the thickness of the second hardmask layer 1510 is from about 50 Angstrom to about 400 Angstrom. In some embodiments, the thickness of the second hardmask layer 1510 is from about 5 Å to about 100 Å. The second hardmask layer 1510 is formed by a suitable deposition process, such as an ALD process, a CVD process, a PVD process, another suitable deposition process, or a combination thereof. Examples of materials for the second hardmask layer 1510 include, but are not limited to, SiN, SiCN, SiC, SiO_(x), SiCO_(x), TiN, TiO, TaN, or a combination thereof. In some embodiments, the deposition process is conducted at a temperature of about 50° C. to about 450° C.

FIG. 16A is a schematic sectional top view illustrating another stage in the fabrication of the semiconductor structure 1300 according to the method 1200 of FIG. 12, FIG. 16B is a schematic sectional view taken on line 16B-16B′ of FIG. 16A, and FIG. 16C is a schematic sectional view taken on line 16C-16C′ of FIG. 16A. In FIGS. 16A-16C, portions of the second hardmask layer 1510 are removed, leaving portions of the second hardmask layer 1510 within the opening in patterned first hardmask layer 1340. In some embodiments, the second hardmask layer 1510 disposed on the top surface of the first hardmask layer 1340 and the second hardmask layer 1510 that is on the IMD layer 1330 are removed, leaving the second hardmask layer 1510 that is on the surrounding wall 1490 of the first hardmask layer 1340 to form an opening in the patterned second hardmask layer 1510. The opening includes three spaced apart holes (a hole 1670 a, a hole 1670 b, and a hole 1670 c). In some embodiments, the holes 1670 a, 1670 b, and 1670 c have a substantially same hole pitch as the holes 1470 a, 1470 b, 1470 c in the patterned first hardmask layer 1340 and a hole width less than the hole width of the holes 1470 a, 1470 b, 1470 c in the patterned first hardmask layer 1340. In some embodiments, the holes 1670 a, 1670 b, 1670 c in the second hardmask layer 1510 have a hole width of about 100 Å to about 700 Å. The portions of the second hardmask layer 1510 (for example, on the top surface of the first hardmask layer 1340 and on the IMD layer 1330) are removed using an etching process (for example, an etch back process). The etching process is a dry etching process, another suitable anisotropic etching process, or a combination thereof. The etching process uses SCF₄, CH_(x)F_(y), C₄F₈, Cl₂, O₂, N₂, Ar, CH₄, another etching gas, or a combination thereof. In some embodiments, the etching process is conducted at a pressure of about 5 mTorr to about 50 mTorr. In some embodiments, the etching process is conducted at a bias voltage of about 10 V to about 50 V.

FIG. 17A is a schematic sectional top view illustrating another stage in the fabrication of the semiconductor structure 1300 according to the method 1200 of FIG. 12, FIG. 17B is a schematic sectional view taken on line 17B-17B′ of FIG. 17A, and FIG. 17C is a schematic sectional view taken on line 17C-17C′ of FIG. 17A. In FIGS. 17A-17C, the opening in patterned second hardmask layer 1510 is transferred to the IMD layer 1330. For example, an opening is formed through the IMD layer 1330. The opening includes three spaced apart holes (a hole 1770 a, a hole 1770 b, and a hole 1770 c) formed through the IMD layer 1330. In some embodiments, the holes 1770 a, 1770 b, 1770 c in the IMD layer 1330 are disposed, such that centers thereof are substantially collinear. An etching process is performed to remove portions of the IMD layer 1330, forming the holes 1770 a, 1770 b, 1770 c that respectively expose conductive lines 1320 a, 1320 b, 1320 c. The etching process uses the first hardmask layer 1340 and the second hardmask layer 1510 as an etching mask. In some embodiments, the holes 1770 a, 1770 b, 1770 c in the IMD layer 1330 have a substantially same hole pitch and a substantially same hole width as the holes 1670 a, 1670 b, 1670 c in the patterned second hardmask layer 1510. After patterning the IMD layer 1330 (for example, to form the holes 1770 a, 1770 b, 1770 c in the IMD layer 1330), the first hardmask layer 1340 and the second hardmask layer 1510 are removed by an etching process. The etching process is a wet etch process, a dry etch process, another suitable etch process, or a combination thereof.

Following the removal of the first hardmask layer 1340 and the second hardmask layer 1510, the opening in the IMD layer 1330 (for example, holes 1770 a, 1770 b, 1770 c) may be filled with a conductive material. In some embodiments, a sputtering process forms a conductive material over IMD layer 1330 that fills the holes 1770 a, 1770 b, 1770 c. In some embodiments, the conductive material is Al, Cu, Ni, another metal material, or a combination thereof. Thereafter, a chemical mechanical planarizing (CMP) process may be performed to remove the excess conductive material, such as conductive material formed on a top surface of the IMD layer 1330. The conductive material remaining in the holes 1770 a, 1770 b, 1770 c serves as vertical interconnects. For example, in some embodiments, the semiconductor structure 1300 can include vertical interconnects formed in the IMD layer 1330, such as a vertical interconnect (formed by conductive material filling the hole 1770 a) to conductive line 1320 a, a vertical interconnect (formed by conductive material filling the hole 1770 b) to conductive line 1320 b, and a vertical interconnect (formed by conductive material filling the hole 1770 c) to conductive line 1320 c.

FIG. 18 is another exemplary flowchart illustrating a method 1800 for fabricating a semiconductor structure according to various aspects of the present disclosure. At block 1810, an IMD layer is provided. At block 1820, a hardmask layer is formed over the IMD layer. At block 1830, a patterned photoresist layer is formed over the hardmask layer. The patterned photoresist layer has an opening formed therethrough, where the opening includes three holes and a pair of channels, each of which interconnects an adjacent pair of the holes. A surrounding wall (formed by the patterned photoresist layer) defines the holes and the channels in the patterned photoresist layer. At block 1840, a chemical layer is formed over the patterned photoresist layer. In some embodiments, the chemical layer is formed on a top surface of the photoresist layer and a surface of the patterned photoresist layer that forms the surrounding wall. The chemical layer has an opening that forms three spaced apart holes extending through the chemical layer. At block 1850, an etching process is performed on the hardmask layer using the chemical layer as an etching mask. The etching process forms an opening in the hardmask layer, where the opening includes three spaced apart holes. At block 1860, the patterned photoresist layer and the chemical layer are removed. At block 1870, an etching process is performed on the IMD layer using the hardmask layer as an etching mask. The etching process forms an opening in the IMD layer, where the opening includes three spaced apart holes that extend through the IMD layer (for example, to a metallization layer). At block 1880, the hardmask layer is removed. Additional steps can be provided before, during, and after method 1800, and some of the steps described can be moved, replaced, or eliminated for additional embodiments of method 1800.

FIG. 19A is a schematic sectional top view illustrating a stage in the fabrication of an exemplary semiconductor structure 1900 according to the method 1800 of FIG. 18, FIG. 19B is a schematic sectional view taken on line 19B-19B′ of FIG. 19A, and FIG. 19C is a schematic sectional view taken on line 19C-19C′ of FIG. 19A. The semiconductor structure 1900 includes a metallization layer formed over a substrate (not shown), where the metallization layer includes an insulative layer 1910 and a plurality of conductive lines (for example, a conductive line 1920 a a conductive line 1920 b, and a conductive line 1920 c). The insulative layer 1910 has a top surface and a bottom surface, where conductive lines 1920 a, 1920 b, 1920 c extend through the insulative layer from the bottom surface to the top surface. Examples of materials for the insulative layer 1910 include, but are not limited to, SiC, SiCO, SiCN, another insulative material, or a combination thereof. In some embodiments, conductive lines 1920 a, 1920 b, 1920 c are formed in the insulative layer 1910 by forming a plurality of holes (openings) through the insulative layer 1910 (for example, extending from the top surface to the bottom surface of the insulative layer 1910), and filling the holes in the insulative layer 1910 (for example, by a sputtering process) with a conductive material, whereby the conductive material forms the conductive lines 1920 a, 1920 b, 1920 c. Examples of conductive material include, but are not limited to, Al, Cu, Ni, another metal material, polysilicon, or a combination thereof. In some embodiments, the conductive lines 1920 a, 1920 b, 1920 c are metal lines or poly lines, depending on design requirements for semiconductor structure 1900. The conductive lines 1920 a, 1920 b, 1920 c are used to interconnect devices (for example, transistors, resistors, capacitors, diodes, and/or other active and/or passive devices) underlying the metallization layer.

An IMD layer 1930 is formed over the metallization layer (here, the insulative layer 1910 and the conductive lines 1920 a, 1920 b, 1920 c). The IMD layer 1930 is formed by a suitable deposition process, such as a CVD process, a PVD process, an ALD process, another deposition process, a derivative thereof, or a combination thereof. The IMD layer 1930 may be formed of low-k dielectric materials, such as carbon-containing low-k dielectric materials, which may further include silicon, oxygen, nitrogen, or a combination thereof.

As shown in FIG. 19B and FIG. 19C, a hardmask layer 1940 and a tri-layer resist stack 1950 are formed in succession over the IMD layer 1930. The hardmask layer 1940 is formed using a suitable deposition process, such as a CVD process, a PVD process, an ALD process, another deposition process, a derivative thereof, or a combination thereof. Examples of materials for the hardmask layer 1940 include, but are not limited to, SiN, SiCN, SiC, SiO_(x), TiN, TiO, TaN, or a combination thereof. The tri-layer resist stack 1950 includes a bottom layer 1950 a, a middle layer 1950 b, and a patterned photoresist layer 1960. In some embodiments, the bottom layer 1950 a is an organic film, and the middle layer 1950 b is a spin-on glass (SOG) layer. In some embodiments, the bottom layer 1950 a is deposited by a spin-on process over the hardmask layer 1940 to provide, for example, anti-reflective properties and etch-stop functionality. In some embodiments, the middle layer 1950 b is formed by depositing (for example, by a spin-on process) SiO₂ over the bottom layer 1950 a.

An opening is formed through the patterned photoresist layer 1960. In FIG. 19A, the opening includes three holes (a hole 1970 a, a hole 1970 b, and a hole 1970 c) that are sequentially disposed along the length of the patterned photoresist layer 1960, a channel 1980 a that interconnects the hole 1970 a and the hole 1970 b, and a channel 1980 b that interconnects the hole 1970 b and the hole 1970 c. A surrounding wall 1990 (defined by the patterned photoresist layer 1960) defines the holes 1970 a, 1970 b, 1970 c and the channels 1980 a, 1980 b in the patterned resist layer 1960. In some embodiments, the holes 1970 a, 1970 b, 1970 c in the patterned photoresist layer 1960 have a hole pitch of about 300 Å to about 1,000 Å and a hole width of about 200 Å to about 800 Å. In some embodiments, the channels 1980 a, 1980 b in the patterned photoresist layer 1960 have a channel width of about 100 Å to about 500 Å. The patterned photoresist layer 1960 is formed using a lithographic process. The lithographic process includes coating (for example, spin-on coating), soft baking, mask aligning, exposure, post exposure baking, developing, rinsing, drying (for example, hard baking), and other processes. Following the formation of the patterned photoresist layer 1960, an ADI process can be performed, in which the patterned photoresist layer 1960 is inspected for defects. If during the ADI process the patterned photoresist layer 1960 is found to be defective, the patterned photoresist layer 1960 is stripped, and the lithographic process is repeated to form a new patterned photoresist layer.

FIG. 20A is a schematic sectional top view illustrating another stage in the fabrication of the semiconductor structure 1900 according to the method 1800 of FIG. 18, FIG. 20B is a schematic sectional view taken on line 20B-20B′ of FIG. 20A, and FIG. 20C is a schematic sectional view taken on line 20C-20C′ of FIG. 20A. In FIGS. 20A-20C, a chemical layer 2010 having an opening therein is formed over the patterned photoresist layer 1960. The opening includes a pair of spaced apart holes (a hole 2070 a, a hole 2070 b, and a hole 2070 b) defined by the chemical layer 2010. For example, the chemical layer 2010 is formed on exposed surfaces of the patterned photoresist layer 1960, such as a top surface of the patterned photoresist layer 1960 and a surface of the patterned photoresist layer 1960 that defines the surrounding wall 1990. In some embodiments, the holes 2070 a, 2070 b, 2070 c have a substantially same hole pitch as the holes 1970 a, 1970 b, 1970 c in the patterned photoresist layer 1960. In some embodiments, the holes 2070 a, 2070 b, 2070 c (defined in the chemical layer 2010) have a hole width less than the hole width of the holes 1970 a, 1970 b, 1970 c in the patterned photoresist layer 2060. In some embodiments, the holes 2070 a, 2070 b, 2070 c have a hole width of about 100 Å to about 700 Å. In some embodiments, as depicted in FIG. 20B and FIG. 20C, the chemical layer 2010 on the top surface of the patterned photoresist layer 1960 has a substantially same thickness as the chemical layer 2010 on the surface of the patterned photoresist layer 1960 that defines the surrounding wall 1990. In some embodiments, the chemical layer 2010 has a thickness at least half of the channel width of the channels 1980 a, 1980 b in the patterned photoresist layer 1960. In some embodiments, the thickness of the chemical layer 2010 is about 50 Å to about 400 Å.

The chemical layer 2010 is formed by any suitable process. In some embodiments, forming the chemical layer 2010 includes: forming a shrink material over exposed portions of the tri-layer resist stack 1950 (for example, over exposed portions of the patterned photoresist layer 1960 and exposed portions of the middle layer 1950 b, such that the shrink material fills the holes 1970 a, 1970 b, 1970 c defined in the patterned photoresist layer 1960); baking the shrink material, such that the shrink material reacts with the patterned photoresist layer 1960 to form the chemical layer 2010; and removing an unreacted portion of the shrink material (for example, portions of the shrink material on the middle layer 1950 b), such that the holes 2070 a, 2070 b, 2070 c are formed through the chemical layer 2010. In some embodiments, the shrink material is formed over the patterned photoresist layer 1960 and middle layer 1950 b (for example, over the holes 1970 a, 1970 b, 1970 c defined in the patterned photoresist layer 1960) using a suitable spin-on process. In some embodiments, the shrink material is baked at a baking temperature of about 110° C. to about 170° C. In some embodiments, the shrink material is baked for about 60 seconds. The unreacted portion of the shrink material is removed using a suitable development process. In some embodiments, the development process includes a puddle development process (for example, where the unreacted portion of the shrink material is washed away with water (for example, de-ionized water (DIW) for about 60 seconds)), an immersion development process, a spray development process, another suitable development process, or a combination thereof. The shrink material includes an inorganic material (such as a dielectric material), an organic material (such as a polymeric material), or a combination thereof. In some embodiments, an example of a water soluble organic material that may be used as the shrink material is commercially available from Dow Chemical Corporation or JSR Corporation. In some embodiments, the shrink material is a topaz-type material, such as that commercially available from Applied Materials, Santa Clara, Calif. In some embodiments, the shrink material is an inter-mixing type polymer.

FIG. 21A is a schematic top view illustrating another stage in the fabrication of the semiconductor structure 1900 according to the method 1800 of FIG. 18, FIG. 21B is a schematic sectional view taken on line 21B-21B′ of FIG. 21A, and FIG. 21C is a schematic sectional view taken on line 21C-21C′ of FIG. 21A. In FIGS. 21A-21C, the opening in patterned chemical layer 2010 is transferred to the hardmask layer 1940. For example, an opening is formed through the hardmask layer 1940. In FIG. 21A, the opening includes three spaced apart holes (a hole 2170 a, a hole 2170 b, and a hole 2170 c). In some embodiments, an etching process is performed to remove portions of the middle layer 1950 b, the bottom layer 1950 a, and the hardmask layer 1940 to expose the IMD layer 1930. The etching process uses the patterned chemical layer 2010 as an etching mask. As such, the holes 2170 a, 2170 b, 2170 c in the patterned hardmask layer 1940 have a substantially same hole pitch and a substantially same hole width as the holes 2070 a, 2070 b, 2070 c in the chemical layer 2010. The etching process is a dry etching process, another suitable anisotropic etching process, or a combination thereof. The etching process uses SCF₄, CH_(x)F_(y), C₄F₈, Cl₂, O₂, N₂, Ar, CH₄, another etching gas, or a combination thereof. In some embodiments, the etching process is conducted at a pressure of about 5 mTorr to about 50 mTorr. In some embodiments, the etching process is conducted at a bias voltage of about 10 V to about 50 V. After patterning the hardmask layer 1940 (for example, following the formation of the holes 2170 a, 2170 b, 2170 c in the hardmask layer 1940), the tri-layer resist stack 1950 is removed by a strip process, thereby removing the chemical layer 2010. In an example, the strip process is a wet strip process and is performed using, for example, hydrofluoric acid (HF). In another example, the strip process is a dry strip process and is performed using, for example, CH₃ or BF₃.

FIG. 22A is a schematic top view illustrating another stage in the fabrication of the semiconductor structure 1900 according to the method 1800 of FIG. 18, FIG. 22B is a schematic sectional view taken on line 22B-22B′ of FIG. 22A, and FIG. 22C is a schematic sectional view taken on line 22C-22C′ of FIG. 22A. In FIGS. 22A-22C, the opening in patterned hardmask layer 1940 is transferred to the IMD layer 1930. For example, an opening is formed through the IMD layer 1930. The opening includes three spaced apart holes (a hole 2270 a, a hole 2270 b, and a hole 2270 c) formed through the IMD layer 1930. In some embodiments, the holes 2270 a, 2270 b, 2270 c in the IMD layer 1930 are disposed, such that centers thereof are substantially collinear. An etching process is performed to remove portions of the IMD layer 1930, forming the holes 2270 a, 2270 b, 2270 c that respectively expose conductive lines 1920 a, 1920 b, 1920 c. The etching process uses the hardmask layer 1940 as an etching mask. In some embodiments, the holes 2270 a, 2270 b, 2270 c in the IMD layer 1930 have a substantially same hole pitch and a substantially same hole width as the holes 2170 a, 2170 b, 2170 c in the patterned hardmask layer 1940. After patterning the IMD layer 1930 (for example, to form the holes 2270 a, 2270 b, 2270 c in the IMD layer 1930), the hardmask layer 1940 is removed by an etching process. The etching process is a wet etch process, a dry etch process, another suitable etch process, or a combination thereof.

Following the removal of the hardmask layer 1940, the opening in the IMD layer 1930 (for example, holes 2270 a, 2270 b, 2270 c) may be filled with a conductive material. In some embodiments, a sputtering process forms a conductive material over the IMD layer 1930 that fills the holes 2270 a, 2270 b, 2270 c. In some embodiments, the conductive material is Al, Cu, Ni, another metal material, or a combination thereof. Thereafter, a chemical mechanical planarizing (CMP) process may be performed to remove the excess conductive material, such as conductive material formed on a top surface of the IMD layer 1930. The conductive material remaining in the holes 2270 a, 2270 b, 2270 c serves as vertical interconnects. For example, in some embodiments, the semiconductor structure 1900 can include vertical interconnects formed in the IMD layer 1930, such as a vertical interconnect (formed by conductive material filling the hole 2270 a) to conductive line 1920 a, a vertical interconnect (formed by conductive material filling the hole 2270 b) to conductive line 1920 b, and a vertical interconnect (formed by conductive material filling the hole 2270 c) to conductive line 1920 c.

FIG. 23 is another exemplary flowchart illustrating a method 2300 for fabricating a semiconductor structure according to various aspects of the present disclosure. At block 2310, an IMD layer is provided. At block 2320, a first hardmask layer is formed over the IMD layer. At block 2330, a patterned photoresist layer is formed over the first hardmask layer. The patterned photoresist layer has an opening formed therethrough, where the opening includes three holes and a channel that interconnects the holes. At block 2340, an etching process is performed on the first hardmask layer using the patterned photoresist layer as an etching mask. The etching process forms an opening through the first hardmask layer, where the opening includes three holes and a channel that interconnects the holes. A surrounding wall (formed by the patterned first hardmask layer) defines the holes and the channel in the first hardmask layer. At block 2350, the patterned photoresist layer is removed. At block 2360, a second hardmask layer is formed on the surrounding wall of the first hardmask layer. The second hardmask layer has an opening that forms three spaced apart holes defined in the second hardmask layer. At block 2370, an etching process is performed on the IMD layer using the first hard mask layer and the second hardmask layer as an etching mask. The etching process forms an opening in the IMD layer, where the opening includes three spaced apart holes that extend through the IMD layer (for example, to a metallization layer). At block 2380, the first hardmask layer and the second hardmask layer are removed. Additional steps can be provided before, during, and after method 2300, and some of the steps described can be moved, replaced, or eliminated for additional embodiments of method 2300.

FIG. 24A is a schematic sectional top view illustrating a stage in the fabrication of an exemplary semiconductor structure 2400 according to the method 2300 of FIG. 23, and FIG. 24B is a schematic sectional view taken on line 24B-24B′ of FIG. 24A. The semiconductor structure 2400 includes a metallization layer formed over a substrate (not shown), where the metallization layer includes an insulative layer 2410 and a plurality of conductive lines (for example, conductive lines 2420). The insulative layer 2410 has a top surface and a bottom surface, where conductive lines 2420 extend through the insulative layer 2410 from the bottom surface to the top surface. Examples of materials for the insulative layer 2410 include, but are not limited to, SiC, SiCO, SiCN, another insulative material, or a combination thereof. In some embodiments, conductive lines 2420 are formed in the insulative layer 2410 by forming a plurality of holes (openings) through the insulative layer 2410 (for example, extending from the top surface to the bottom surface of the insulative layer 2410), and filling the holes in the insulative layer 2410 (for example, by a sputtering process) with a conductive material, whereby the conductive material forms the conductive lines 2420. Examples of conductive material include, but are not limited to, Al, Cu, Ni, another metal material, polysilicon, or a combination thereof. In some embodiments, the conductive lines 2420 are metal lines or poly lines, depending on design requirements for semiconductor structure 2400. The conductive lines 2420 are used to interconnect devices (for example, transistors, resistors, capacitors, diodes, and/or other active and/or passive devices) underlying the metallization layer.

An IMD layer 2430 is formed over the metallization layer (here, insulative layer 2410 and conductive lines 2420). The IMD layer 2430 is formed by a suitable deposition process, such as a CVD process, a PVD process, an ALD process, another deposition process, a derivative thereof, or a combination thereof. The IMD layer 2430 may be formed of low-k dielectric materials, such as carbon-containing low-k dielectric materials, which may further include silicon, oxygen, nitrogen, or a combination thereof.

As shown in FIG. 24B, a first hardmask layer 2440 and a tri-layer resist stack 2450 are formed in succession over the IMD layer 2430. The first hardmask layer 2440 is formed using a suitable deposition process, such as a CVD process, a PVD process, an ALD process, another deposition process, a derivative thereof, or a combination thereof. Examples of materials for the first hardmask layer 2440 include, but are not limited to, SiN, SiCN, SiC, SiO_(x), TiN, TiO, TaN, or a combination thereof. The tri-layer resist stack 2450 includes a bottom layer 2450 a, a middle layer 2450 b, and a patterned photoresist layer 2460. In some embodiments, the bottom layer 2450 a is an organic film, and the middle layer 2450 b is a spin-on glass (SOG) layer. In some embodiments, the bottom layer 2450 a is deposited by a spin-on process over the first hardmask layer 2440 to provide, for example, anti-reflective properties and etch-stop functionality. In some embodiments, the middle layer 2450 b is formed by depositing (for example, by a spin-on process) SiO₂ over the bottom layer 2450 a.

An opening is formed through the patterned photoresist layer 2460. In FIG. 24A, the opening includes three holes (a hole 2470 a, a hole 2470 b, and a hole 2470 c) and a channel 2480 that interconnects the holes 2470 a, 2470 b, 2470 c. A surrounding wall 2490 (defined by the patterned photoresist layer 2460) defines the holes 2470 a, 2470 b, 2470 c and the channel 2480 in the patterned photoresist layer 2460. The channel 2480 includes a first section that interconnects the hole 2470 a and the hole 2470 b and a second section that interconnects the first section and the hole 2470 c. In some embodiments, the holes 2470 a, 2470 b, 2470 c in the patterned photoresist layer 2460 have a hole pitch of about 300 Å to about 1,000 Å and a hole width of about 200 Å to about 800 Å. In some embodiments, the first section and the second section of the channel 2480 in the patterned photoresist layer 2460 have a channel width of about 100 Å to about 500 Å. The patterned photoresist layer 2460 is formed using a lithographic process. The lithographic process includes coating (for example, spin-on coating), soft baking, mask aligning, exposure, post exposure baking, developing, rinsing, drying (for example, hard baking), and other processes. Following the formation of the patterned photoresist layer 2460, an ADI process can be performed, in which the patterned photoresist layer 2460 is inspected for defects. If during the ADI process the patterned photoresist layer 2460 is found to be defective, the patterned photoresist layer 2460 is stripped, and the lithographic process is repeated to form a new patterned photoresist layer.

FIG. 25A is a schematic sectional top view illustrating another stage in the fabrication of the semiconductor structure 2400 according to the method 2300 of FIG. 23, and FIG. 25B is a schematic sectional view taken on line 25B-25B′ of FIG. 25A. In FIG. 25A and FIG. 25B, the opening in patterned photoresist layer 2460 is transferred to the first hardmask layer 2440. For example, an opening is formed through the first hardmask layer 2440. In FIG. 25A, the opening includes three holes (a hole 2570 a, a hole 2570 b, and a hole 2570 c) and a channel 2580 that interconnects the holes 2570 a, 2570 b, 2570 c. A surrounding wall 2590 (defined by the patterned first hardmask layer 2440) defines the holes 2570 a, 2570 b, 2570 c and the channel 2580 in the patterned first hardmask layer 2440. The channel 2580 includes a first section that interconnects the hole 2570 a and the hole 2570 b and a second section that interconnects the first section and the hole 2570 c. In some embodiments, centers of the holes 2570 a, 2570 b, 2570 c in the first hardmask layer 2440 are disposed at vertices of a triangle. In some embodiments, an etching process is performed to remove portions of the middle layer 2450 b, the bottom layer 2450 a, and the first hardmask layer 2440 to expose the IMD layer 2430. The etching process uses the patterned photoresist layer 2460 as an etching mask. As such, the holes 2570 a, 2570 b, 2570 c in the first hardmask layer 2440 have a substantially same hole pitch and a substantially same hole width as the holes 2470 a, 2470 b, 2470 c in the patterned photoresist layer 2460, and the channel 2580 in the first hardmask layer 2440 have a substantially same channel width as the channel 2480 in the patterned photoresist layer 2460. The etching process is a dry etching process, another suitable anisotropic etching process, or a combination thereof. The etching process uses SCF₄, CH_(x)F_(y), C₄F₈, Cl₂, O₂, N₂, Ar, CH₄, another etching gas, or a combination thereof. In some embodiments, the etching process is conducted at a pressure of about 5 mTorr to about 50 mTorr. In some embodiments, the etching process is conducted at a bias voltage of about 10 Volts to about 50 Volts. After patterning the first hardmask layer 2440 (for example, following the formation of the holes 2570 a, 2570 b, 2570 c and the channel 2580 in the first hardmask layer 2440), the tri-layer resist stack 2450 is removed by a strip process. In an example, the strip process is a wet strip process and is performed using, for example, hydrofluoric acid (HF). In another example, the strip process is a dry strip process and is performed using, for example, CH₃ or BF₃.

FIG. 26A is a schematic sectional top view illustrating another stage in the fabrication of the semiconductor structure 2400 according to the method 2300 of FIG. 23, and FIG. 26B is a schematic sectional view taken on line 26B-26B′ of FIG. 26A. In FIG. 26A and FIG. 26B, a second hardmask layer 2610 is formed over the first hardmask layer 2440 and the IMD layer 2430. As shown in FIG. 26B, the second hardmask layer 2610 is formed over the first hardmask layer 2440 and the IMD layer 2430 in a conformal manner. That is, the second hardmask layer 2610 that is on a top surface of the first hardmask layer 2440, the second hardmask layer 2610 that is on the surrounding wall 2590 of the first hardmask layer 2440, and the second hardmask layer 2610 that is on the IMD layer 2430, in an exemplary embodiment, all have a substantially same thickness. In some embodiments, the second hardmask layer 2610 has a thickness at least half of the channel width of the channel 2580 in the first hardmask layer 2440, and thus the second hardmask layer 2610 fills the channel 2580 in the first hardmask layer 2440. In an exemplary embodiment, the thickness of the second hardmask layer 2610 is from about 50 Å to about 400 Å. In some embodiments, the thickness of the second hardmask layer 1510 is from about 5 Å to about 100 Å. The second hardmask layer 2610 is formed by a suitable deposition process, such as an ALD process, a CVD process, a PVD process, another suitable deposition process, or a combination thereof. Examples of materials for the second hardmask layer 2610 include, but are not limited to, SiN, SiCN, SiC, SiO_(x), SiCO_(x), TiN, TiO, TaN, or a combination thereof. In some embodiments, the deposition process is conducted at a temperature of about 50° C. to about 450° C.

FIG. 27A is a schematic sectional top view illustrating another stage in the fabrication of the semiconductor structure 2400 according to the method 2300 of FIG. 23, and FIG. 27B is a schematic sectional view taken on line 27B-27B′ of FIG. 27A. In FIG. 27A and FIG. 27B, portions of the second hardmask layer 2610 are removed, leaving portions of the second hardmask layer 2610 within the opening in patterned first hardmask layer 2440. In some embodiments, the second hardmask layer 2610 disposed on the top surface of the first hardmask layer 2440 and the second hardmask layer 2610 that is on the IMD layer 2430 are removed, leaving the second hardmask layer 2610 that is on the surrounding wall 2590 of the first hardmask layer 2440 to form an opening in the patterned second hardmask layer 2610. The opening includes three spaced apart holes (a hole 2770 a, a hole 2770 b, and a hole 2770 c). In some embodiments, the holes 2770 a, 2770 b, and 2770 c have a substantially same hole pitch as the holes 2570 a, 2570 b, 2570 c in the patterned first hardmask layer 2440 and a hole width less than the hole width of the holes 2570 a, 2570 b, 2570 c in the patterned first hardmask layer 2440. In some embodiments, the holes 2770 a, 2770 b, 2770 c in the second hardmask layer 2610 have a hole width of about 100 Å to about 700 Å. The portions of the second hardmask layer 2610 (for example, on the top surface of the first hardmask layer 2440 and on the IMD layer 2430) are removed using an etching process (for example, an etch back process). The etching process is a dry etching process, another suitable anisotropic etching process, or a combination thereof. The etching process uses SCF₄, CH_(x)F_(y), C₄F₈, Cl₂, O₂, N₂, Ar, CH₄, another etching gas, or a combination thereof. In some embodiments, the etching process is conducted at a pressure of about 5 mTorr to about 50 mTorr. In some embodiments, the etching process is conducted at a bias voltage of about 10 V to about 50 V.

FIG. 28A is a schematic sectional top view illustrating another stage in the fabrication of the semiconductor structure 2400 according to the method 2300 of FIG. 23, and FIG. 28B is a schematic sectional view taken on line 28B-28B′ of FIG. 28A. In FIG. 28A and FIG. 28B, the opening in patterned second hardmask layer 2610 is transferred to the IMD layer 2430. For example, an opening is formed through the IMD layer 2430. The opening includes three spaced apart holes (a hole 2870 a, a hole 2870 b, and a hole 2870 c) formed through the IMD layer 2430. In some embodiments, the holes 2870 a, 2870 b, 2870 c in the IMD layer 2430 are disposed, such that centers of the holes 2870 a, 2870 b, 2870 c are disposed at vertices of a triangle. An etching process is performed to remove portions of the IMD layer 2430, forming the holes 2870 a, 2870 b, 2870 c that respectively expose conductive lines 2420. The etching process uses the first hardmask layer 2440 and the second hardmask layer 2610 as an etching mask. In some embodiments, the holes 2870 a, 2870 b, 2870 c in the IMD layer 2430 have a substantially same hole pitch and a substantially same hole width as the holes 2770 a, 2770 b, 2770 c in the patterned second hardmask layer 2610. After patterning the IMD layer 2430 (for example, to form the holes 2870 a, 2870 b, 2870 c in the IMD layer 2430), the first hardmask layer 2440 and the second hardmask layer 2610 are removed by an etching process. The etching process is a wet etch process, a dry etch process, another suitable etch process, or a combination thereof.

Following the removal of the first hardmask layer 2440 and the second hardmask layer 2610, the opening in the IMD layer 2430 (for example, holes 2870 a, 2870 b, 2870 c) may be filled with a conductive material. In some embodiments, a sputtering process forms a conductive material over IMD layer 2430 that fills the holes 2870 a, 2870 b, 2870 c. In some embodiments, the conductive material is Al, Cu, Ni, another metal material, or a combination thereof. Thereafter, a chemical mechanical planarizing (CMP) process may be performed to remove the excess conductive material, such as conductive material formed on a top surface of the IMD layer 2430. The conductive material remaining in the holes 2870 a, 2870 b, 2870 c serves as vertical interconnects. For example, in some embodiments, the semiconductor structure 2400 can include vertical interconnects formed in the IMD layer 2430, such as vertical interconnects (formed by conductive material filling the holes 2870 a, 2870 b, 2870 c) to conductive lines 2420.

FIG. 29 is another exemplary flowchart illustrating a method 2900 for fabricating a semiconductor device according to various aspects of the present disclosure. At block 2910, an IMD layer is provided. At 2920, a hardmask layer is formed over the IMD layer. At block 2930, a patterned photoresist layer is formed over the hardmask layer. The patterned photoresist layer has an opening formed therethrough, where the opening includes three holes and a channel that interconnects the holes. A surrounding wall (formed by the patterned photoresist layer) defines the holes and the channel in the patterned photoresist layer. At block 2940, a chemical layer is formed over the patterned photoresist layer. In some embodiments, the chemical layer is formed on a top surface of the patterned photoresist layer and a surface of the patterned photoresist layer that defines the surrounding wall. The chemical layer has an opening that includes three spaced apart holes extending through the chemical layer. At block 2950, an etching process is performed on the hardmask layer using the chemical layer as an etching mask. The etching process forms an opening through the hardmask layer, where the opening includes three spaced apart holes. At block 2960, the patterned photoresist layer and the chemical layer are removed. At block 2970, an etching process is performed on the IMD layer using the hardmask layer as an etching mask. The etching process forms an opening in the IMD layer, where the opening includes three spaced apart holes that extend through the IMD layer (for example, to a metallization layer). At 2980, the hardmask layer is removed. Additional steps can be provided before, during, and after method 2900, and some of the steps described can be moved, replaced, or eliminated for additional embodiments of method 2900.

FIG. 30A is a schematic sectional top view illustrating a stage in the fabrication of an exemplary semiconductor structure 3000 according to the method 2900 of FIG. 29, and FIG. 30B is a schematic sectional view taken on line 30B-30B′ of FIG. 30A. The semiconductor structure 3000 includes a metallization layer formed over a substrate (not shown), where the metallization layer includes an insulative layer 3010 and a plurality of conductive lines (for example, conductive lines 3020). The insulative layer 3010 has a top surface and a bottom surface, where conductive lines 3020 extend through the insulative layer 3010 from the bottom surface to the top surface. Examples of materials for the insulative layer 3010 include, but are not limited to, SiC, SiCO, SiCN, another insulative material, or a combination thereof. In some embodiments, the conductive lines 3020 are formed in the insulative layer 3010 by forming a plurality of holes (openings) through the insulative layer 3010 (for example, extending from the top surface to the bottom surface of the insulative layer 3010), and filling the holes in the insulative layer 3010 (for example, by a sputtering process) with a conductive material, whereby the conductive material forms the conductive lines 3020. Examples of conductive material include, but are not limited to, Al, Cu, Ni, another metal material, polysilicon, or a combination thereof. In some embodiments, the conductive lines 3020 are metal lines or poly lines, depending on design requirements for semiconductor structure 3000. The conductive lines 3020 are used to interconnect devices (for example, transistors, resistors, capacitors, diodes, and/or other active and/or passive devices) underlying the metallization layer.

An IMD layer 3030 is formed over the metallization layer (here, insulative layer 3010 and conductive lines 3020). The IMD layer 3030 is formed by a suitable deposition process, such as a CVD process, a PVD process, an ALD process, another deposition process, a derivative thereof, or a combination thereof. The IMD layer 3030 may be formed of low-k dielectric materials, such as carbon-containing low-k dielectric materials, which may further include silicon, oxygen, nitrogen, or a combination thereof.

As shown in FIG. 30B, a hardmask layer 3040 and a tri-layer resist stack 3050 are formed in succession over the IMD layer 3030. The hardmask layer 3040 is formed using a suitable deposition process, such as a CVD process, a PVD process, an ALD process, another deposition process, a derivative thereof, or a combination thereof. Examples of materials for the hardmask layer 3040 include, but are not limited to, SiN, SiCN, SiC, SiO,, TiN, TiO, TaN, or a combination thereof. The tri-layer resist stack 3050 includes a bottom layer 3050 a, a middle layer 3050 b, and a patterned photoresist layer 3060. In some embodiments, the bottom layer 3050 a is an organic film, and the middle layer 3050 b is a spin-on glass (SOG) layer. In some embodiments, the bottom layer 3050 a is deposited by a spin-on process over the hardmask layer 3040 to provide, for example, anti-reflective properties and etch-stop functionality. In some embodiments, the middle layer 3050 b is formed by depositing (for example, by a spin-on process) SiO₂ over the bottom layer 3050 a.

An opening is formed through the patterned photoresist layer 3060. In FIG. 30A, the opening includes three holes (a hole 3070 a, a hole 3070 b, and a hole 3070 c) and a channel 3080 that interconnects the holes 3070 a, 3070 b, 3070 c. A surrounding wall 3090 (defined by the patterned photoresist layer 3060) defines the holes 3070 a, 3070 b, 3070 c and the channel 3080 in the patterned photoresist layer 3060. The channel 3080 includes a first section that interconnects the hole 3070 a and the hole 3070 b and a second section that interconnects the first section and the hole 3070 c. In some embodiments, the holes 3070 a, 3070 b, 3070 c in the patterned photoresist layer 3060 have a hole pitch of about 300 Å to about 1,000 Å and a hole width of about 200 Å to about 800 Å. In some embodiments, the first section and the second section of the channel 3080 in the patterned photoresist layer 3060 have a channel width of about 100 Å to about 500 Å. The patterned photoresist layer 3060 is formed using a lithographic process. The lithographic process includes coating (for example, spin-on coating), soft baking, mask aligning, exposure, post exposure baking, developing, rinsing, drying (for example, hard baking), and other processes. Following the formation of the patterned photoresist layer 3060, an ADI process can be performed, in which the patterned photoresist layer 3060 is inspected for defects. If during the ADI process the patterned photoresist layer 3060 is found to be defective, the patterned photoresist layer 3060 is stripped, and the lithographic process is repeated to form a new patterned photoresist layer.

FIG. 31A is a schematic sectional top view illustrating another stage in the fabrication of the semiconductor structure 3000 according to the method 2900 of FIG. 29, and FIG. 31B is a schematic sectional view taken on line 31B-31B′ of FIG. 31A. In FIG. 31A and FIG. 31B, a chemical layer 3110 is formed over the patterned photoresist layer 3060, such that three spaced apart holes (a hole 3170 a, a hole 3170 b, and a hole 3170 c) are defined by the chemical layer 3110. For example, the chemical layer 3110 is formed on exposed surfaces of the patterned photoresist layer 3060, such as a top surface of the patterned photoresist layer 3060 and a surface of the patterned photoresist layer 3060 that defines the surrounding wall 3090. In some embodiments, the holes 3170 a, 3170 b, 3170 c have a substantially same hole pitch as the holes 3070 a, 3070 b, 3070 c in the patterned photoresist layer 3060. In some embodiments, the holes 3170 a, 3170 b, 3170 c (defined in the chemical layer 3110) have a hole width less than the hole width of the holes 3070 a, 3070 b, 3070 c in the patterned photoresist layer 3060. In some embodiments, the holes 3170 a, 3170 b, 3170 c have a hole width of about 100 Å to about 700 Å. In some embodiments, as depicted in FIG. 31B, the chemical layer 3110 on the top surface of the patterned photoresist layer 3060 has a substantially same thickness as the chemical layer 3110 on the surface of the patterned photoresist layer 3060 that defines the surrounding wall 3090. In some embodiments, the chemical layer 3110 has a thickness at least half of the channel width of the channel 3080 in the patterned photoresist layer 3060. In some embodiments, the thickness of the chemical layer 3110 is about 50 Å to about 400 Å.

The chemical layer 3110 is formed by any suitable process. In some embodiments, forming the chemical layer 3110 includes: forming a shrink material over exposed portions of the tri-layer resist stack 3050 (for example, over exposed portions of the patterned photoresist layer 3060 and exposed portions of the middle layer 3050 b, such that the shrink material fills the holes 3070 a, 3070 b, 3070 c defined in the patterned photoresist layer 3060); baking the shrink material, such that the shrink material reacts with the patterned photoresist layer 860 to form the chemical layer 3110; and removing an unreacted portion of the shrink material (for example, portions of the shrink material on the middle layer 3050 b), such that the holes 3170 a, 3170 b, 3170 c are formed through the chemical layer 3110. In some embodiments, the shrink material is formed over the patterned photoresist layer 3060 and middle layer 3050 b (for example, over the holes 3070 a, 3070 b, 3070 c defined in the patterned photoresist layer 3060) using a suitable spin-on process. In some embodiments, the shrink material is baked at a baking temperature of about 110° C. to about 170° C. In some embodiments, the shrink material is baked for about 60 seconds. The unreacted portion of the shrink material is removed using a suitable development process. In some embodiments, the development process includes a puddle development process (for example, where the unreacted portion of the shrink material is washed away with water (for example, de-ionized water (DIW) for about 60 seconds)), an immersion development process, a spray development process, another suitable development process, or a combination thereof. The shrink material includes an inorganic material (such as a dielectric material), an organic material (such as a polymeric material), or a combination thereof. In some embodiments, an example of a water soluble organic material that may be used as the shrink material is commercially available from Dow Chemical Corporation or JSR Corporation. In some embodiments, the shrink material is a topaz-type material, such as that commercially available from Applied Materials, Santa Clara, Calif. In some embodiments, the shrink material is an inter-mixing type polymer.

FIG. 32A is a schematic top view illustrating another stage in the fabrication of the semiconductor structure 3000 according to the method 2900 of FIG. 29, and FIG. 32B is a schematic sectional view taken on line 32B-32B′ of FIG. 32A. In FIG. 32A and FIG. 32B, the opening in the patterned chemical layer 3110 is transferred to the hardmask layer 3040. For example, an opening is formed through the hardmask layer 3040. In FIG. 32A, the opening includes three spaced apart holes (a hole 3270 a, a hole 3270 b, and a hole 3270 c). In some embodiments, an etching process is performed to remove portions of the middle layer 3050 b, the bottom layer 3050 a, and the hardmask layer 3040 to expose the IMD layer 3030. The etching process uses the patterned chemical layer 3110 as an etching mask. As such, the holes 3270 a, 3270 b, 3270 c in the patterned hardmask layer 3040 have a substantially same hole pitch and a substantially same hole width as the holes 3170 a, 3170 b, 3170 c in the chemical layer 3110. The etching process is a dry etching process, another suitable anisotropic etching process, or a combination thereof. The etching process uses SCF₄, CH_(x)F_(y), C₄F₃₀, Cl₂, O₂, N₂, Ar, CH₄, another etching gas, or a combination thereof. In some embodiments, the etching process is conducted at a pressure of about 5 mTorr to about 50 mTorr. In some embodiments, the etching process is conducted at a bias voltage of about 10 V to about 50 V. After patterning the hardmask layer 3040 (for example, following the formation of the holes 3270 a, 3270 b, 3270 c in the hardmask layer 3040), the tri-layer resist stack 3050 is removed by a strip process, thereby removing the chemical layer 3110. In an example, the strip process is a wet strip process and is performed using, for example, hydrofluoric acid (HF). In another example, the strip process is a dry strip process and is performed using, for example, CH₃ or BF₃.

FIG. 33A is a schematic top view illustrating another stage in the fabrication of the semiconductor structure 3000 according to the method 2900 of FIG. 29, and FIG. 33B is a schematic sectional view taken on line 33B-33B′ of FIG. 33A. In FIG. 33A and FIG. 33B, the opening in patterned hardmask layer 3040 is transferred to the IMD layer 3030. For example, an opening is formed through the IMD layer 3030. The opening includes three spaced apart holes (a hole 3370 a, a hole 3370 b, a hole 3370 c) formed through the IMD layer 3030. In some embodiments, the holes 3370 a, 3370 b, 3370 c in the IMD layer 3030 are disposed, such that centers of the holes 3370 a, 3370 b, 3370 c in the IMD layer 3030 are disposed at vertices of a triangle. An etching process is performed to remove portions of the IMD layer 3030, forming the holes 3370 a, 3370 b, 3370 c that respectively expose conductive lines 3020. The etching process uses the hardmask layer 3040 as an etching mask. In some embodiments, the holes 3370 a, 3370 b, 3370 c in the IMD layer 3030 have a substantially same hole pitch and a substantially same hole width as the holes 3270 a, 3270 b, 3270 c in the patterned hardmask layer 3040. After patterning the IMD layer 3030 (for example, to form the holes 3370 a, 3370 b, 3370 c in the IMD layer 3030), the hardmask layer 3040 is removed by an etching process. The etching process is a wet etch process, a dry etch process, another suitable etch process, or a combination thereof.

Following the removal of the hardmask layer 3040, the opening in the IMD layer 3030 (for example, holes 3370 a, 3370 b, 3370 c) may be filled with a conductive material. In some embodiments, a sputtering process forms a conductive material over the IMD layer 3030 that fills the holes 3370 a, 3370 b, 3370 c. In some embodiments, the conductive material is Al, Cu, Ni, another metal material, or a combination thereof. Thereafter, a chemical mechanical planarizing (CMP) process may be performed to remove the excess conductive material, such as conductive material formed on a top surface of the IMD layer 3030. The conductive material remaining in the holes 3370 a, 3370 b, 3370 c serves as vertical interconnects. For example, in some embodiments, the semiconductor structure 3000 can include vertical interconnects formed in the IMD layer 3030, such as vertical interconnects (formed by conductive material filling the holes 3370 a, 3370 b, 3370 c) to conductive lines 3020.

It is noted openings (having one or more holes) formed in the insulative layers 210, 810, 1310, 1910, 2410, 3010, which are subsequently filled with conductive material to form the conductive lines disposed in the insulative layers 210, 810, 1310, 1910, 2410, 3010, may be formed using the processes as described above with reference to FIGS. 2A-6C, FIGS. 8A-11C, FIGS. 13A-17C, FIGS. 19A-22C, FIGS. 24A-28C, and FIGS. 30A-33B, respectively.

In accordance with some embodiments, a method for fabricating a semiconductor structure provides a dielectric layer and a patterned photoresist layer is formed over the dielectric layer. An opening (hole) is formed in the patterned photoresist layer, and in some embodiments, the opening extends through the patterned photoresist layer. In some embodiments, a surrounding wall of the patterned photoresist layer defines the opening, where the surrounding wall has a generally peanut-shaped cross section.

In accordance with some embodiments, a method for fabricating a semiconductor structure provides a dielectric layer and a patterned photoresist layer is formed over the dielectric layer. An opening is formed in the patterned photoresist layer, and in some embodiments, the opening extends through the patterned photoresist layer. In some embodiments, the opening includes at least a pair of holes and at least one channel. The at least one channel interconnects the at least the pair of holes.

In accordance with some embodiments, a tri-layer resist stack includes a bottom layer, a middle layer, and a patterned photoresist layer. The middle layer is disposed over the bottom layer, and the patterned photoresist layer is disposed over the middle layer. An opening (hole) is formed in the patterned photoresist layer, and in some embodiments, the opening extends through the patterned photoresist layer. In some embodiments, a surrounding wall of the patterned photoresist layer defines the opening, where the surrounding wall has a generally peanut-shaped cross section.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. A method of fabricating a semiconductor structure, comprising: providing a dielectric layer; and forming a patterned photoresist layer over the dielectric layer, the patterned photoresist layer being formed with a hole therethrough defined by a surrounding wall, wherein the surrounding wall of the patterned photoresist layer has a generally peanut-shaped cross section.
 2. The method of claim 1, further comprising forming a chemical layer on a top surface and the surrounding wall of the patterned photoresist layer to form a pair of spaced apart holes defined by the chemical layer.
 3. The method of claim 2, wherein the chemical layer has a thickness at least half of a width of a middle section of the hole in the patterned photoresist layer.
 4. The method of claim 2, wherein the forming the chemical layer includes: forming a shrink material over the patterned photoresist layer and the dielectric layer, performing a baking process on the shrink material to react the shrink material with the patterned photoresist layer, whereby the reacted shrink material forms the chemical layer, and removing unreacted shrink material.
 5. The method of claim 4, wherein the shrink material is baked at a temperature of about 110° C. to about 170° C. and for about 60 seconds.
 6. The method of claim 2, further comprising performing an etching process on the dielectric layer using the chemical layer as an etching mask to form a pair of spaced apart holes through the dielectric layer.
 7. A method of fabricating a semiconductor structure, comprising: providing a dielectric layer; and forming a patterned photoresist layer over the dielectric layer, the patterned photoresist layer being formed therethrough with at least a pair of holes and at least one channel that interconnects the at least a pair of holes.
 8. The method of claim 7, further comprising: forming a first hardmask layer disposed between the dielectric layer and the patterned photoresist layer; and performing an etching process on the first hardmask layer using the patterned photoresist layer as an etching mask to form at least a pair of holes and at least one channel that interconnects the at least a pair of holes through the first hardmask layer.
 9. The method of claim 8, wherein the at least a pair of holes and the at least one channel in the first hardmask layer are defined by a surrounding wall of the first hardmask layer, the method further comprising forming a second hardmask layer on the surrounding wall of the first hardmask layer to form at least a pair of spaced apart holes defined by the second hardmask layer.
 10. The method of claim 9, wherein the second hardmask layer has a thickness at least half of a width of the at least one channel in the first hardmask layer.
 11. The method of claim 9, wherein the forming the second hardmask layer includes: forming the second hardmask layer over the first hardmask layer and the dielectric layer, and removing the second hardmask layer that is on the dielectric layer.
 12. The method of claim 9, further comprising performing an etching process on the dielectric layer using the second hardmask layer as an etching mask to form at least a pair of spaced apart holes through the dielectric layer.
 13. The method of claim 7, wherein the patterned photoresist layer includes a surrounding wall that defines the at least a pair of holes and the at least one channel therein, the method further comprising forming a chemical layer on a top surface and the surrounding wall of the patterned photoresist layer to form a pair of spaced apart holes defined by the chemical layer.
 14. The method of claim 13, wherein the chemical layer has a thickness at least half of a width of the at least one channel in the patterned photoresist layer.
 15. The method of claim 13, further comprising performing an etching process on the dielectric layer using the chemical layer as an etching mask to form a pair of spaced apart holes through the dielectric layer.
 16. The method of claim 13, wherein the forming the chemical includes: forming a shrink material over the patterned photoresist layer and the dielectric layer, performing a baking process on the shrink material to react the shrink material with the patterned photoresist layer, whereby the reacted shrink material forms the chemical layer, and removing unreacted shrink material.
 17. The method of claim 16, wherein the shrink material is baked at a temperature of about 110° C. to about 170° C. and for about 60 seconds.
 18. The method of claim 13, the method further comprising forming a hardmask layer that is disposed between the dielectric layer and the patterned photoresist layer; and performing an etching process on the hardmask layer using the chemical layer as an etching mask to form at least a pair of spaced apart holes through the hardmask layer.
 19. The method of claim 18, further comprising performing an etching process on the dielectric layer using the hardmask layer as an etching mask to form at least a pair of spaced apart holes through the dielectric layer.
 20. A tri-layer resist stack, comprising: a bottom layer; a middle layer disposed over the bottom layer; and a patterned photoresist layer disposed over the middle layer and formed with a hole therethrough, wherein the hole in the patterned photoresist layer is defined by a surrounding wall that has a generally peanut-shaped cross section. 